# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
This module defines structured units and quantities.
"""
from __future__ import annotations # For python < 3.10
# Standard library
import operator
import numpy as np
from .core import UNITY, Unit, UnitBase
__all__ = ["StructuredUnit"]
DTYPE_OBJECT = np.dtype("O")
def _names_from_dtype(dtype):
"""Recursively extract field names from a dtype."""
names = []
for name in dtype.names:
subdtype = dtype.fields[name][0].base
if subdtype.names:
names.append([name, _names_from_dtype(subdtype)])
else:
names.append(name)
return tuple(names)
def _normalize_names(names):
"""Recursively normalize, inferring upper level names for unadorned tuples.
Generally, we want the field names to be organized like dtypes, as in
``(['pv', ('p', 'v')], 't')``. But we automatically infer upper
field names if the list is absent from items like ``(('p', 'v'), 't')``,
by concatenating the names inside the tuple.
"""
result = []
for name in names:
if isinstance(name, str) and len(name) > 0:
result.append(name)
elif (
isinstance(name, list)
and len(name) == 2
and isinstance(name[0], str)
and len(name[0]) > 0
and isinstance(name[1], tuple)
and len(name[1]) > 0
):
result.append([name[0], _normalize_names(name[1])])
elif isinstance(name, tuple) and len(name) > 0:
new_tuple = _normalize_names(name)
name = "".join([(i[0] if isinstance(i, list) else i) for i in new_tuple])
result.append([name, new_tuple])
else:
raise ValueError(
f"invalid entry {name!r}. Should be a name, "
"tuple of names, or 2-element list of the "
"form [name, tuple of names]."
)
return tuple(result)
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class StructuredUnit:
"""Container for units for a structured Quantity.
Parameters
----------
units : unit-like, tuple of unit-like, or `~astropy.units.StructuredUnit`
Tuples can be nested. If a `~astropy.units.StructuredUnit` is passed
in, it will be returned unchanged unless different names are requested.
names : tuple of str, tuple or list; `~numpy.dtype`; or `~astropy.units.StructuredUnit`, optional
Field names for the units, possibly nested. Can be inferred from a
structured `~numpy.dtype` or another `~astropy.units.StructuredUnit`.
For nested tuples, by default the name of the upper entry will be the
concatenation of the names of the lower levels. One can pass in a
list with the upper-level name and a tuple of lower-level names to
avoid this. For tuples, not all levels have to be given; for any level
not passed in, default field names of 'f0', 'f1', etc., will be used.
Notes
-----
It is recommended to initialize the class indirectly, using
`~astropy.units.Unit`. E.g., ``u.Unit('AU,AU/day')``.
When combined with a structured array to produce a structured
`~astropy.units.Quantity`, array field names will take precedence.
Generally, passing in ``names`` is needed only if the unit is used
unattached to a `~astropy.units.Quantity` and one needs to access its
fields.
Examples
--------
Various ways to initialize a `~astropy.units.StructuredUnit`::
>>> import astropy.units as u
>>> su = u.Unit('(AU,AU/day),yr')
>>> su
Unit("((AU, AU / d), yr)")
>>> su.field_names
(['f0', ('f0', 'f1')], 'f1')
>>> su['f1']
Unit("yr")
>>> su2 = u.StructuredUnit(((u.AU, u.AU/u.day), u.yr), names=(('p', 'v'), 't'))
>>> su2 == su
True
>>> su2.field_names
(['pv', ('p', 'v')], 't')
>>> su3 = u.StructuredUnit((su2['pv'], u.day), names=(['p_v', ('p', 'v')], 't'))
>>> su3.field_names
(['p_v', ('p', 'v')], 't')
>>> su3.keys()
('p_v', 't')
>>> su3.values()
(Unit("(AU, AU / d)"), Unit("d"))
Structured units share most methods with regular units::
>>> su.physical_type
((PhysicalType('length'), PhysicalType({'speed', 'velocity'})), PhysicalType('time'))
>>> su.si
Unit("((1.49598e+11 m, 1.73146e+06 m / s), 3.15576e+07 s)")
"""
def __new__(cls, units, names=None):
dtype = None
if names is not None:
if isinstance(names, StructuredUnit):
dtype = names._units.dtype
names = names.field_names
elif isinstance(names, np.dtype):
if not names.fields:
raise ValueError("dtype should be structured, with fields.")
dtype = np.dtype([(name, DTYPE_OBJECT) for name in names.names])
names = _names_from_dtype(names)
else:
if not isinstance(names, tuple):
names = (names,)
names = _normalize_names(names)
if not isinstance(units, tuple):
units = Unit(units)
if isinstance(units, StructuredUnit):
# Avoid constructing a new StructuredUnit if no field names
# are given, or if all field names are the same already anyway.
if names is None or units.field_names == names:
return units
# Otherwise, turn (the upper level) into a tuple, for renaming.
units = units.values()
else:
# Single regular unit: make a tuple for iteration below.
units = (units,)
if names is None:
names = tuple(f"f{i}" for i in range(len(units)))
elif len(units) != len(names):
raise ValueError("lengths of units and field names must match.")
converted = []
for unit, name in zip(units, names):
if isinstance(name, list):
# For list, the first item is the name of our level,
# and the second another tuple of names, i.e., we recurse.
unit = cls(unit, name[1])
name = name[0]
else:
# We are at the lowest level. Check unit.
unit = Unit(unit)
if dtype is not None and isinstance(unit, StructuredUnit):
raise ValueError(
"units do not match in depth with field "
"names from dtype or structured unit."
)
converted.append(unit)
self = super().__new__(cls)
if dtype is None:
dtype = np.dtype(
[
((name[0] if isinstance(name, list) else name), DTYPE_OBJECT)
for name in names
]
)
# Decay array to void so we can access by field name and number.
self._units = np.array(tuple(converted), dtype)[()]
return self
def __getnewargs__(self):
"""When de-serializing, e.g. pickle, start with a blank structure."""
return (), None
@property
def field_names(self):
"""Possibly nested tuple of the field names of the parts."""
return tuple(
([name, unit.field_names] if isinstance(unit, StructuredUnit) else name)
for name, unit in self.items()
)
# Allow StructuredUnit to be treated as an (ordered) mapping.
def __len__(self):
return len(self._units.dtype.names)
def __getitem__(self, item):
# Since we are based on np.void, indexing by field number works too.
return self._units[item]
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def values(self):
return self._units.item()
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def keys(self):
return self._units.dtype.names
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def items(self):
return tuple(zip(self._units.dtype.names, self._units.item()))
def __iter__(self):
yield from self._units.dtype.names
# Helpers for methods below.
def _recursively_apply(self, func, cls=None):
"""Apply func recursively.
Parameters
----------
func : callable
Function to apply to all parts of the structured unit,
recursing as needed.
cls : type, optional
If given, should be a subclass of `~numpy.void`. By default,
will return a new `~astropy.units.StructuredUnit` instance.
"""
applied = tuple(func(part) for part in self.values())
# Once not NUMPY_LT_1_23: results = np.void(applied, self._units.dtype).
results = np.array(applied, self._units.dtype)[()]
if cls is not None:
return results.view((cls, results.dtype))
# Short-cut; no need to interpret field names, etc.
result = super().__new__(self.__class__)
result._units = results
return result
def _recursively_get_dtype(self, value, enter_lists=True):
"""Get structured dtype according to value, using our field names.
This is useful since ``np.array(value)`` would treat tuples as lower
levels of the array, rather than as elements of a structured array.
The routine does presume that the type of the first tuple is
representative of the rest. Used in ``_get_converter``.
For the special value of ``UNITY``, all fields are assumed to be 1.0,
and hence this will return an all-float dtype.
"""
if enter_lists:
while isinstance(value, list):
value = value[0]
if value is UNITY:
value = (UNITY,) * len(self)
elif not isinstance(value, tuple) or len(self) != len(value):
raise ValueError(f"cannot interpret value {value} for unit {self}.")
descr = []
for (name, unit), part in zip(self.items(), value):
if isinstance(unit, StructuredUnit):
descr.append(
(name, unit._recursively_get_dtype(part, enter_lists=False))
)
else:
# Got a part associated with a regular unit. Gets its dtype.
# Like for Quantity, we cast integers to float.
part = np.array(part)
part_dtype = part.dtype
if part_dtype.kind in "iu":
part_dtype = np.dtype(float)
descr.append((name, part_dtype, part.shape))
return np.dtype(descr)
@property
def si(self):
"""The `StructuredUnit` instance in SI units."""
return self._recursively_apply(operator.attrgetter("si"))
@property
def cgs(self):
"""The `StructuredUnit` instance in cgs units."""
return self._recursively_apply(operator.attrgetter("cgs"))
# Needed to pass through Unit initializer, so might as well use it.
def _get_physical_type_id(self):
return self._recursively_apply(
operator.methodcaller("_get_physical_type_id"), cls=Structure
)
@property
def physical_type(self):
"""Physical types of all the fields."""
return self._recursively_apply(
operator.attrgetter("physical_type"), cls=Structure
)
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def decompose(self, bases=set()):
"""The `StructuredUnit` composed of only irreducible units.
Parameters
----------
bases : sequence of `~astropy.units.UnitBase`, optional
The bases to decompose into. When not provided,
decomposes down to any irreducible units. When provided,
the decomposed result will only contain the given units.
This will raises a `UnitsError` if it's not possible
to do so.
Returns
-------
`~astropy.units.StructuredUnit`
With the unit for each field containing only irreducible units.
"""
return self._recursively_apply(operator.methodcaller("decompose", bases=bases))
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def is_equivalent(self, other, equivalencies=[]):
"""`True` if all fields are equivalent to the other's fields.
Parameters
----------
other : `~astropy.units.StructuredUnit`
The structured unit to compare with, or what can initialize one.
equivalencies : list of tuple, optional
A list of equivalence pairs to try if the units are not
directly convertible. See :ref:`unit_equivalencies`.
The list will be applied to all fields.
Returns
-------
bool
"""
try:
other = StructuredUnit(other)
except Exception:
return False
if len(self) != len(other):
return False
for self_part, other_part in zip(self.values(), other.values()):
if not self_part.is_equivalent(other_part, equivalencies=equivalencies):
return False
return True
def _get_converter(self, other, equivalencies=[]):
if not isinstance(other, type(self)):
other = self.__class__(other, names=self)
converters = [
self_part._get_converter(other_part, equivalencies=equivalencies)
for (self_part, other_part) in zip(self.values(), other.values())
]
def converter(value):
if not hasattr(value, "dtype"):
value = np.array(value, self._recursively_get_dtype(value))
result = np.empty_like(value)
for name, converter_ in zip(result.dtype.names, converters):
result[name] = converter_(value[name])
# Index with empty tuple to decay array scalars to numpy void.
return result if result.shape else result[()]
return converter
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def to(self, other, value=np._NoValue, equivalencies=[]):
"""Return values converted to the specified unit.
Parameters
----------
other : `~astropy.units.StructuredUnit`
The unit to convert to. If necessary, will be converted to
a `~astropy.units.StructuredUnit` using the dtype of ``value``.
value : array-like, optional
Value(s) in the current unit to be converted to the
specified unit. If a sequence, the first element must have
entries of the correct type to represent all elements (i.e.,
not have, e.g., a ``float`` where other elements have ``complex``).
If not given, assumed to have 1. in all fields.
equivalencies : list of tuple, optional
A list of equivalence pairs to try if the units are not
directly convertible. See :ref:`unit_equivalencies`.
This list is in addition to possible global defaults set by, e.g.,
`set_enabled_equivalencies`.
Use `None` to turn off all equivalencies.
Returns
-------
values : scalar or array
Converted value(s).
Raises
------
UnitsError
If units are inconsistent
"""
if value is np._NoValue:
# We do not have UNITY as a default, since then the docstring
# would list 1.0 as default, yet one could not pass that in.
value = UNITY
return self._get_converter(other, equivalencies=equivalencies)(value)
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def to_string(self, format="generic"):
"""Output the unit in the given format as a string.
Units are separated by commas.
Parameters
----------
format : `astropy.units.format.Base` instance or str
The name of a format or a formatter object. If not
provided, defaults to the generic format.
Notes
-----
Structured units can be written to all formats, but can be
re-read only with 'generic'.
"""
parts = [part.to_string(format) for part in self.values()]
out_fmt = "({})" if len(self) > 1 else "({},)"
if format.startswith("latex"):
# Strip $ from parts and add them on the outside.
parts = [part[1:-1] for part in parts]
out_fmt = "$" + out_fmt + "$"
return out_fmt.format(", ".join(parts))
def _repr_latex_(self):
return self.to_string("latex")
__array_ufunc__ = None
def __mul__(self, other):
if isinstance(other, str):
try:
other = Unit(other, parse_strict="silent")
except Exception:
return NotImplemented
if isinstance(other, UnitBase):
new_units = tuple(part * other for part in self.values())
return self.__class__(new_units, names=self)
if isinstance(other, StructuredUnit):
return NotImplemented
# Anything not like a unit, try initialising as a structured quantity.
try:
from .quantity import Quantity
return Quantity(other, unit=self)
except Exception:
return NotImplemented
def __rmul__(self, other):
return self.__mul__(other)
def __truediv__(self, other):
if isinstance(other, str):
try:
other = Unit(other, parse_strict="silent")
except Exception:
return NotImplemented
if isinstance(other, UnitBase):
new_units = tuple(part / other for part in self.values())
return self.__class__(new_units, names=self)
return NotImplemented
def __rlshift__(self, m):
try:
from .quantity import Quantity
return Quantity(m, self, copy=False, subok=True)
except Exception:
return NotImplemented
def __str__(self):
return self.to_string()
def __repr__(self):
return f'Unit("{self.to_string()}")'
def __eq__(self, other):
try:
other = StructuredUnit(other)
except Exception:
return NotImplemented
return self.values() == other.values()
def __ne__(self, other):
if not isinstance(other, type(self)):
try:
other = StructuredUnit(other)
except Exception:
return NotImplemented
return self.values() != other.values()
class Structure(np.void):
"""Single element structure for physical type IDs, etc.
Behaves like a `~numpy.void` and thus mostly like a tuple which can also
be indexed with field names, but overrides ``__eq__`` and ``__ne__`` to
compare only the contents, not the field names. Furthermore, this way no
`FutureWarning` about comparisons is given.
"""
# Note that it is important for physical type IDs to not be stored in a
# tuple, since then the physical types would be treated as alternatives in
# :meth:`~astropy.units.UnitBase.is_equivalent`. (Of course, in that
# case, they could also not be indexed by name.)
def __eq__(self, other):
if isinstance(other, np.void):
other = other.item()
return self.item() == other
def __ne__(self, other):
if isinstance(other, np.void):
other = other.item()
return self.item() != other
def _structured_unit_like_dtype(
unit: UnitBase | StructuredUnit, dtype: np.dtype
) -> StructuredUnit:
"""Make a `StructuredUnit` of one unit, with the structure of a `numpy.dtype`.
Parameters
----------
unit : UnitBase
The unit that will be filled into the structure.
dtype : `numpy.dtype`
The structure for the StructuredUnit.
Returns
-------
StructuredUnit
"""
if isinstance(unit, StructuredUnit):
# If unit is structured, it should match the dtype. This function is
# only used in Quantity, which performs this check, so it's fine to
# return as is.
return unit
# Make a structured unit
units = []
for name in dtype.names:
subdtype = dtype.fields[name][0]
if subdtype.names is not None:
units.append(_structured_unit_like_dtype(unit, subdtype))
else:
units.append(unit)
return StructuredUnit(tuple(units), names=dtype.names)
